The invention relates to a method for transporting articles to a station, in particular preforms to a blow-molding apparatus, wherein each article has a protrusion and is moved by a drive means along a guide, and also to an apparatus for this purpose.
According to the current prior art, articles are conveyed to a subsequent processing device either via gravitational methods having a roller sorter and an elevated chute (WO 02/36466 A1) or are oriented by centrifugal methods on a rotating disk or ring and conveyed to the subsequent processing station by means of an actively driven conveyor section or the like (WO 2004/069700 A1, US 2008/0113055 A1, EP 1 690 813 A1).
For example, U.S. Pat. No. 7,322,458 B1 shows the possibility of singularizing the individual articles in chambers which are disposed on conveyor belts.
According to DE 10 2009 016 593 A1, singularizing takes place in a cell-wheel-like transfer device.
In US 2008/0142337 A1, individual preforms are placed between circulating belts, wherein two belts serve to orient the preforms and a belt located therebeneath serves for transport.
According to US 2008/0142339 A1, preforms are singularized in cavities of a transport wheel.
The closest prior art is shown by EP 1 690 813 A1, according to which preforms or similar articles pass onto a turntable and are trapped in a circumferential slot between the directing walls and the turntable.
In all of the known apparatuses and methods, as the speeds become increasingly high (30 000 to 80 000 preforms per hour and more), large fluctuations in the process speed occur, resulting in long buffer sections upstream of the subsequent processing machine, for example the blow-molding machine. Furthermore, malfunctioning or stoppage of the plant on account of wrongly oriented and/or jammed preforms occurs. Previously, attempts were made to stabilize the process, to eliminate the disruptive elements and to control/regulate this delicate and highly dynamic process by means of expensive sensors and complicated regulation means. It has been shown, in particular in all centrifugal methods, that it is particularly difficult technically to ensure that preforms which leave the disk or the ring are also correctly oriented and positioned. Furthermore, local accumulations of preforms occur in the event of overfeed on the disk or ring, and these disrupt the orientation of the preforms thereby making the output of the disk insufficient. If the overfeed lasts too long, this often results in overfilling of the disk or ring and finally in the failure of the system.
It has furthermore been shown that at conveying rates above about 60 000 preforms per hour, the reactivity/reaction rate of these regulation mechanisms and the inertia of the system become critical. A further problem is that of removing a homogeneously fed quantity of preforms from a storage container which contains the preforms as bulk material and supplying this quantity to the following system. Freshly unpackaged preforms have high mutual adhesion and this can result in the formation of clusters and accumulation of preforms. Consequently, such feeding and supply systems usually convey the preforms in a highly discontinuous manner in pulses and clusters.
A further problem is that the blow-molding process for PET bottle production sometimes forces the immediate stoppage of the preform supply to the stretch blow-molding machine on account of faults. The stretch blow-molding machine continues to operate at full speed (desired value) but without blow-molding bottles (no-load operation). After the fault has been eliminated, the process is immediately resumed at the desired value without a start-up ramp. At high conveying rates, the inertia of the supply system often causes difficulties such that long buffer sections are again required in order to compensate said difficulties. As the conveying rates become increasingly high (60 000 preforms per hour and more), this can virtually no longer be achieved reliably.
The object of the present invention is to remedy the abovementioned disadvantages and to develop a method and an apparatus of the abovementioned type, which is distinguished by very high efficiency and simplicity, in particular stands out on account of self-regulating behavior of the system, which are dynamically adapted, control/regulate themselves, remain continuously in operation and smooth and homogenize the flow of preforms, thereby allowing high reliability and reactivity at high conveying rates. The whole is also intended to be realizable in a cost-effective manner.